X-Rays are extremely high energy Photons which have enough energy to pass through dense material(as with Gamma rays), this allows most X-Rays to pass through the body, with extra dense part(bones etc) to absorb them.

I'm not sure how this relates in terms of the Energy Gap though; you should e-mail such questions to sixtysymbols@hotmail.co.uk and I'm sure Brady will pass them on to the Professors.

A ton of other videos can be found at www.sixtysymbols.com too, and chemistry based videos are also found at http://www.periodicvideos.com/

All answers are given by staff at The University of Nottingham (UK), I'm a student there and have been(and still currently being) taught by most of the people in these Physics videos and it's great seeing people so amazed by some of the stuff they say in their videos, their lectures are always as good too!

>> ^bamdrew:

hey, lets talk about x-rays!
skin is boring; I want to see skeletons!

>> ^xxovercastxx:

@<a rel="nofollow" href="http://videosift.com/member/Estuffing17" title="member since May 2nd, 2010" class="profilelink">Estuffing17
Actually, because visible green light is at a higher energy level than red light, if an objects energy gap is high enough to let green light through, then red light will also pass through because it has even lower energy levels, not the other way around.
That's exactly what I said in my example.
As far as a translucent green material is concerned, when we perceive an object to have color, it is because that objects atoms are arranged in such a way that it reflects that wavelength of light (green in this case) back to our eye, while either absorbing, refracting or letting pass through photons of other wavelengths. Just because a piece of glass is green does not mean it will not allow other higher and lower energy photons to pass through it.
Green glass, as I understand it, is green because it's filtering out other colors. It's a simplified example, yes. Obviously you can have a little yellow or blue or whatever mixed in and it still looks "green".
But the energy gap explanation seems to mean that "green" glass would be letting all red, orange, and yellow light through since they are lower energy levels. It's one thing to say a little bit of another color is coming through and it's imperceptible. If all the "weaker" colors are coming through along with the green, it doesn't seem to me like it would look very green.


All the light at all the energy levels will pass through the material, you're right. But the extra bit that makes this make sense is that this isn't the only thing happening. You've seen a simple explanation of one thing. The other wavelengths of light are passing through the material, but not all in a straight line. Their paths are diverted and dispersed so you don't get a meaningful amount of these wavelengths of light entering your eye.

This is the reason the sky is blue. Light is refracted by particles in the substance through which it is traveling. The closer the wavelength of the light is to the particles it's being refracted by, the more it's course is altered. The blue end of the spectrum has the closest wavelength to the size of particles in the air.

When you look at the sky with your back to the sun, the light that makes it to your eyes will obviously have had to have it's path altered a lot by the particles in the air. Only the wavelengths that are closest to the size of the particles in the air will be altered this much, hence the sky looking blue.

The lower the sun, the more air there is for the light to pass through and the more the other wavelengths will be refracted. At midday on the equator the sun in a white dot surrounded by blue. There isn't enough air between you and the sun to cause anything other than the blue light to be refracted back to your eye, so if you're not looking at the sun (not good...) you're only going to see blue. At sunset there is a lot more air between you and the sun, enough for the longer wavelengths to be affected, hence the red colours spreading away from the sun causing the firey sunsets we all love.

So, to sum up; just because all the wavelengths of light can pass through something it doesn't necessarily follow that they aren't affected in any way at all. They can pass through but have their paths altered, hence the different colours you see.

I'd love a fuller explanation of this. How do the particles affect the protons? What makes them alter course?

He said that the light was monochromatic, so it is just that wavelength and not a spectrum.

^xxovercastxx:

@<a rel="nofollow" href="http://videosift.com/member/Estuffing17" title="member since May 2nd, 2010" class="profilelink">Estuffing17
Actually, because visible green light is at a higher energy level than red light, if an objects energy gap is high enough to let green light through, then red light will also pass through because it has even lower energy levels, not the other way around.
That's exactly what I said in my example.
As far as a translucent green material is concerned, when we perceive an object to have color, it is because that objects atoms are arranged in such a way that it reflects that wavelength of light (green in this case) back to our eye, while either absorbing, refracting or letting pass through photons of other wavelengths. Just because a piece of glass is green does not mean it will not allow other higher and lower energy photons to pass through it.
Green glass, as I understand it, is green because it's filtering out other colors. It's a simplified example, yes. Obviously you can have a little yellow or blue or whatever mixed in and it still looks "green".
But the energy gap explanation seems to mean that "green" glass would be letting all red, orange, and yellow light through since they are lower energy levels. It's one thing to say a little bit of another color is coming through and it's imperceptible. If all the "weaker" colors are coming through along with the green, it doesn't seem to me like it would look very green.

@Estuffing17

Actually, because visible green light is at a higher energy level than red light, if an objects energy gap is high enough to let green light through, then red light will also pass through because it has even lower energy levels, not the other way around.

That's exactly what I said in my example.

As far as a translucent green material is concerned, when we perceive an object to have color, it is because that objects atoms are arranged in such a way that it reflects that wavelength of light (green in this case) back to our eye, while either absorbing, refracting or letting pass through photons of other wavelengths. Just because a piece of glass is green does not mean it will not allow other higher and lower energy photons to pass through it.

Green glass, as I understand it, is green because it's filtering out other colors. It's a simplified example, yes. Obviously you can have a little yellow or blue or whatever mixed in and it still looks "green".

But the energy gap explanation seems to mean that "green" glass would be letting all red, orange, and yellow light through since they are lower energy levels. It's one thing to say a little bit of another color is coming through and it's imperceptible. If all the "weaker" colors are coming through along with the green, it doesn't seem to me like it would look very green.

>> ^Xax:

I don't follow.


Haha, okay. Then how about this: The color of the object involved does not necessarily have an effect on the kind of light that can pass through it. I could find seven different green translucent materials that might all have differing energy gaps, even though they all look green.

>> ^BicycleRepairMan:

>> ^xxovercastxx:
This leaves me with another question, unfortunately.
Let's stick with his example of green being high energy and red being low.
The photon only gets through the material if it's not strong enough to excite an electron. This makes sense for a translucent red material. The material's energy gap could be large enough to allow red light through but block all other.
This does not make sense for translucent green material. If the material's energy gap were large enough to allow green light through, it would also allow red light through, resulting in a translucent yellow material. This would seem to allow only red, orange, and then increasingly grey/colorless shades of yellow.
So what's missing from this explanation?

As I understand it(and I'm not sure I understood the question): Red is on a very low enegy level, so if the "energy gap" is large enough to let red pass, green will also pass, which means the light will be moving towards the white end of the spectrum. This means that if you want to make a translucent green material you need materials that absorbs or displace red (such as green plants)



Actually, because visible green light is at a higher energy level than red light, if an objects energy gap is high enough to let green light through, then red light will also pass through because it has even lower energy levels, not the other way around.

As far as a translucent green material is concerned, when we perceive an object to have color, it is because that objects atoms are arranged in such a way that it reflects that wavelength of light (green in this case) back to our eye, while either absorbing, refracting or letting pass through photons of other wavelengths. Just because a piece of glass is green does not mean it will not allow other higher and lower energy photons to pass through it.

I hope this clarifies things for you a bit!

>> ^BicycleRepairMan:

>> ^xxovercastxx:
This leaves me with another question, unfortunately.
Let's stick with his example of green being high energy and red being low.
The photon only gets through the material if it's not strong enough to excite an electron. This makes sense for a translucent red material. The material's energy gap could be large enough to allow red light through but block all other.
This does not make sense for translucent green material. If the material's energy gap were large enough to allow green light through, it would also allow red light through, resulting in a translucent yellow material. This would seem to allow only red, orange, and then increasingly grey/colorless shades of yellow.
So what's missing from this explanation?

As I understand it(and I'm not sure I understood the question): Red is on a very low enegy level, so if the "energy gap" is large enough to let red pass, green will also pass, which means the light will be moving towards the white end of the spectrum. This means that if you want to make a translucent green material you need materials that absorbs or displace red (such as green plants)


You're addressing the correct question, yes. Does this mean that a translucent green material is a mix of materials with 2 different energy gaps?

>> ^xxovercastxx:

This leaves me with another question, unfortunately.
Let's stick with his example of green being high energy and red being low.
The photon only gets through the material if it's not strong enough to excite an electron. This makes sense for a translucent red material. The material's energy gap could be large enough to allow red light through but block all other.
This does not make sense for translucent green material. If the material's energy gap were large enough to allow green light through, it would also allow red light through, resulting in a translucent yellow material. This would seem to allow only red, orange, and then increasingly grey/colorless shades of yellow.
So what's missing from this explanation?


As I understand it(and I'm not sure I understood the question): Red is on a very low enegy level, so if the "energy gap" is large enough to let red pass, green will also pass, which means the light will be moving towards the white end of the spectrum. This means that if you want to make a translucent green material you need materials that absorbs or displace red (such as green plants)

This leaves me with another question, unfortunately.

Let's stick with his example of green being high energy and red being low.

The photon only gets through the material if it's not strong enough to excite an electron. This makes sense for a translucent red material. The material's energy gap could be large enough to allow red light through but block all other.

This does not make sense for translucent green material. If the material's energy gap were large enough to allow green light through, it would also allow red light through, resulting in a translucent yellow material. This would seem to allow only red, orange, and then increasingly grey/colorless shades of yellow.

So what's missing from this explanation?